Theory-based treatments for reducing anxiety and pain in children undergoing repeated medical procedures are limited; furthermore, little is known about the factors that give rise to anxiety and pain in such settings. This study will apply cognitive-behavioral treatment principles to reduce anticipatory anxiety and, subsequently, procedural anxiety and pain in children undergoing repeated medical procedures. Also, this study will examine how memory, bias and individual difference variables, such as coping style, influence anxiety and pain during medical procedures. Children with cancer from three different age groups will be assigned to either a treatment or an attention-control group. Treatment, based on conditioning principles combined with cognitive influences on conditioning, will encourage children to re-evaluate more positively their previous experiences with medical procedures and decrease reactivity to procedure-related stimuli. It is hypothesized that children receiving treatment will show less self-report, physiological, and behavioral anxiety and pain before and during medical procedures, and that these differences will be maintained at a follow-up assessment. Anxiety will mediate the relationship between treatment condition and pain, and memory bias will mediate the relationship between past and present anxiety and pain during medical procedures. The broad objective of this research is to enhance understanding of and reduce children's pain and fears during repeated cancer procedures.